Forgive me for coming into this debate belatedly.
Let me illustrate what I mean (pun intended) by the following relationship (one suggested by you):
. I live in the United States.
In this sentence the word 'I' is defined, say in a dictionary
Also live is so defined
Also the United States is also so defined
And most of us have attached meaning to those definitions.
The sentence is then a relationship between already defined concepts or symbols.
The sentence does not redefine any of the previously defined symbols.
It instead is akin to an equation that defines (I use this word purposefully) a relationship between the symbols.
So my supposition is that you regard such relationships as definitions.
Then the process I use to catch a ball can be defined as a sequence of events that allow me to place my glove closer and closer to the flight path of the ball. But that is the name of the process. It does not describe the means that I used to get better and better information on where the ball is going.
Sooo---I tend to think of definitions and postulates and assumptions and axioms as basically the same thing, and the relationship between such concepts as relationships. But the one described above about where I live can also be a definition.
Where I need help is then to describe how the process of gathering information to catch a ball can also be thought of as shifting definitions. I would be very pleased if you could help me out in this way.